FRP vessels have long been the standard means for water containment in water treatment, conditioning and filtration applications. FRP tanks are manufactured by several methods with the primary method being termed as “blow mold and wind” methodology. This is the process by which a plastic bottle or liner is blow molded to the required size and configuration and then reinforced for pressure capability by fiberglass filament winding. The continuous strand fiberglass is impregnated with an epoxy resin that serves as the binder between the fiberglass and the tank. The fiberglass is wound around the exterior of the tanks in a controlled method. The amount and pattern by which the fiberglass is applied determines the ultimate performance of the pressure vessels in terms of strength and durability.
Other less utilized techniques for making a FRP pressure vessel center around the various methods for making the plastic liner. They include rotational molding, split shell injection molding, and the welding of injection molded end caps to an extruded sidewall. In all cases, the final plastic bottle is wound with fiberglass to achieve the strength requirements.
The plastic bottle needed for use in the intended applications may have numerous openings. At a minimum, the tank will have one axial opening for the attachment of control valves or other connections for getting fluid in and out of the tank. The size of that opening can vary but in all cases it is smaller than the diameter of the tank. The size of the opening restricts access into the tank thereby limiting the installation of features and accessories.
One of the most desirable accessories is what is called a diffuser plate. Other names associated with a diffuser plate may be nozzle plate, filtration plate, or chamber separator plate. FRP tanks not having an internal diffuser plate have what is called a filter basket in its place. The purpose of the filter basket is to separate the clean fluid from the solid filter media. The filter basket comes in many designs but generally is small so it can be installed in the center of the bottom of the FRP tank. The filter basket is attached to a riser tube, which is a connection between the control valve and the filter basket. All water injected into or drawn from the FRP tank travels through the filter basket and the riser tube. During the cycling of a water softener, water travels through the filter media to perform the softening or cleaning process required.
With the market introduction in 2002 of a tank construction method by which injection molded end caps are welded to an extruded sidewall tube, the industry has started to demand FRP tanks with internal features and accessories. There is a need in the art for more efficient and/or better internal features of a FRP tank.